This invention relates to a solenoid valve.
FIGS. 3 and 4 illustrate the conventional solenoid valve in a side sectional view and a plan view, respectively. In the figures, reference numeral 1 is a casing, 2 is a coil wound around a bobbin 3, 4 is a stationary iron core comprising a stationary portion 4a having a threaded bore having thread engagedly therein an adjustment portion 4b which is adjustable in axial position relative to the stationary portion 4a. The stationary portion 4a and the adjustment portion 4b are secured to each other by calking 4c at the threaded engagement portions. 5 is a plunger magnetically attracted toward the stationary iron core 4 upon the energization of the coil 2, the plunger 5 having at its one end an actuator element 6 opposing to the adjustment portion 4a of the stationary portion 4b of the stationary iron core 4 with a gap S therebetween. 7 is a spring for spring-biasing the plunger 5 in the direction away from the stationary iron core 4, 8 is a valve seat having an opening opened or closed by a vlave end of the plunger 5, 9 and 10 are fluid inlet and outlet ports.
The operation will now be described. The plunger 5 which closes the opening of the valve seat 8 by the spring action of the spring 7 is separated from the valve seat 8 by the magnetic attraction toward the stationary iron core 4 upon the energization of the coil 2. Therefore, by switching on and off the current to the coil 2, the opening of the valve seal 8 can be opened and closed. At this time, the stroke of the plunger 5 is determined by the gap S defined between the stationary iron core 4 and the actuator element 6 of the plunger 5, and the adjustment portion 4b is threaded-engaged into the stationary portion 4a in order to adjust the gap S. The adjustment of the gap S can be achieved by first securing the stationary portion 4a of the stationary iron core 4 to the casing 1 by calking, and then rotating the adjustment portion 4b relative to the stationary portion 4a to adjust the axial dimension of the gap S, and finally forming calking portions 4c at the threaded portion to prevent any rotation of the adjustment portion 4b.
With the conventional solenoid valve as above described, the stationary iron core 4 is composed of the stationary portion 4a and the adjustment portion 4b thread-engaged with the stationary portion 4a. Therefore, the structure is complicated and the adjustment of the gap S requires several steps, such as securing the stationary portion 4a to the casing 1 and rotating the adjustment portion 4b to obtain a desired gap S and further forming calking portions at the threaded portion to prevent undesirable rotation of the adjustment portion 4b, resulting in a complicated gap adjusting process including a number of steps. Also, the precise adjustment of the gap S cannot easily be achieved because a large axial force is applied to the adjustment portion 4b in the direction of movement of the plunger 5, i.e., the direction of adjustment of the gap S during the formation of the calking portions 4c.